Conventionally, there is known a particle filter as a method that tracks a specific target in a video. For example, Patent Document 1 discloses therein an image processing device that reads video data for each frame, generates edge images of image frames, distributes particles in a space of a set of coefficients and a space of shape space vectors, acquires a likelihood observation and a probability density distribution of each particle, and generates, as a track result, a curve which is obtained by performing weighted averaging on each parameter by the probability density distribution.